With the progress which has been made with domestic electrical appliances in recent years the generation of heat has become a problem, and with personal computers the temperature reached as a result of the heat generated by the CPU has risen as higher levels of performance have been achieved. Methods involving the fitting of air-cooling fans have generally been adopted as a counter-measure, but because of miniaturization the fans must be small if they can be used at all, and a box which has a cooling effect even if a fan is not fitted is desirable.
Paint compositions for heat controlling purposes which are characterized by the inclusion of a film-forming component comprising a high condensate which does not include silanol groups of at least one type of compound selected from among the group comprising organosilicon compounds and low-condensates thereof, and mica of particle size not more than 40 μm in an amount of from 100 to 300 parts by weight per 100 parts by weight of said film-forming component and titanium oxide of particle size not more than 1 μm in an amount of from 50 to 200 parts by weight per 100 parts by weight of said film-forming component are known as paint compositions which control heating (for example, see Japanese Examined Patent Publication H6-96682).
However, when this paint is used the titanium oxide and mica are essential components and there is a problem in that they cannot be colored optionally. In particular there is a major weakness in that the provision of black and glitter cannot be achieved for providing design features with color which are essential in the field of domestic electrical appliances.
Furthermore, paint compositions which have excellent heat-radiating properties and electromagnetic wave absorbing properties which are characterized in that they contain as mass % of the solid fraction from 20 to 80% ferrite powder and from 3 to 60% of carbon black powder with the remainder comprising resin, and the amounts of ferrite powder and carbon black powder in the paint are such that 30%≦ferrite powder (%)+carbon black powder (%)≦90% are known as painted metal sheets which have excellent heat-radiating properties and electromagnetic wave absorbing properties (for example, see Japanese Unexamined Patent Application Laid Open 2004-027064).
However, there is a weakness in that the paint film is black because of the carbon black which has been added and it cannot be colored optionally.
Furthermore, painted metal sheets which have excellent heat-radiating properties and coloring properties which have an organic coating layer which contains from 3 to 70 mass % of boron nitride of average particle size from 0.01 to 30 μm of thickness at least 1 μm on at least one side of a metal sheet are known as a means in which carbon black is not used in the top-coat paint. (For example, see Japanese Unexamined Patent Application Laid Open 2005-139535) However, with this method the heat-radiating performance is provided by just the top-coat layer and the heat-radiation properties are poor when compared with a paint film which has a two-layer structure.
Furthermore, heat-radiating surface treated materials which are characterized in that an outer-layer paint film and an inner layer paint film are provided on a base material surface and the inner layer paint film contains from 0.03 to 70 mass % with respect to the dry mass of the inner paint film of a pigment of which the heat reflectance is at least 70%, such as carbon black, alumina, zirconia, titania, silica, zircon, magnesia or the like, are known (for example, see Japanese Unexamined Patent Application Laid Open 2002-228085).
However, with this method there is a weakness in that the thermal emissivity is inevitably lowered by the top-coat paint film.
Furthermore, resin-coated metal sheets where a resin paint film which contains white pigment and/or glitter pigment is coated on one or both of the black colored surfaces of a black colored metal sheet of which one or both sides is black in color and the thickness of said resin paint film is from 0.5 to 10 μm and, moreover, the amount of white pigment and/or glitter pigment which is included in said resin paint film is in total from 1 to 25 mass % and of which the color as an L-value is from 44.0 to 60.0 are known as resin coated metal sheets which have excellent heat-radiating properties as well as scratch resistance and finger-marking resistance (for example, see Japanese Unexamined Patent Application Laid Open 2005-238769).
However, with this method the film thickness of the second layer cannot be great and so there is a weakness in that the satisfactory covering properties which are needed for obtaining designs and multi-colors cannot be maintained.